A bridge amplifier's random noise on the balance signal

PHYSICS · Multi-part · Fermi University Physics · Scientific Practice & Experimental Methods · Electronics, Instrumentation & Communication · Feedback, operational amplifiers and analogue signal processing

Measurement and Method, Ch Designing the measurement: noise, averaging, null and differential methods

Problem

A bridge amplifier's random noise on the balance signal, after averaging for a time

t

, is

k/\sqrt{t}

with

k = 0.060\,\mu\mathrm{V\,s^{1/2}}

. Its zero drifts at a rate

D

as the amplifier warms. ((a)) In an uncontrolled room,

D = 0.15\,\mu\mathrm{V\,s^{-1}}

. Using

u^2(t) = k^2/t + (Dt)^2

, find the optimum averaging time

t_{\rm opt}

and the resulting minimum noise

u_{\rm min}

. ((b)) Once the room is temperature-controlled, the drift falls to

D = 0.030\,\mu\mathrm{V\,s^{-1}}

. Find the new

t_{\rm opt}

and

u_{\rm min}

. ((c)) State how

t_{\rm opt}

and

u_{\rm min}

scale with

D

, and check that the factor-of-5 reduction in

D

produces the ratios your two answers show.

Browse the problem library